Group III-nitride (also referred to as III-nitride or III-N) heterojunction devices can deliver advantageous properties compared to their silicon and gallium arsenic counterparts for power switch applications. The advantageous properties include, but are not limited to, a wide bandgap, a high breakdown electric field, a capability of high-temperature operation and a large thermal conductivity. A wide-bandgap group III-nitride heterostructure device can yield a two-dimensional electron gas (2DEG) channel with a high sheet charge concentration and high electron mobility. Accordingly, group III-nitride devices (e.g. GaN-based heterostructure devices, such as those incorporating AlGaN/GaN heterostructure) have emerged as attractive candidates for high-efficiency, high voltage power driving systems and power converters.
To improve functionality and enhance reliability of these power driving systems and power converters, it is desirable to accommodate not only the high-voltage core power devices, but also the low-voltage peripheral devices that are monolithically integrated on the same group III-nitride for building mixed-signal (e.g., sensing/control/protection) driver circuits.
To turn on a high-voltage core power device, such as high electron mobility transistor (HEMT), its Schottky gate electrode is usually slightly over-driven by the driver circuit to minimize on-resistance and maximize output current. In this way, due to exponential current-voltage relationship of the Schottky gate, overdriving gate voltage of the power device will lead to over-current that result in gate failure. Moreover, in an enhancement-mode HEMT (E-HEMT) that is realized with fluorine plasma-implant technology, the overdrive gate voltage bias beyond the critical voltage (for example, around 2.5V) may introduce threshold voltage instability of the device. Therefore, a gate overdrive protection is necessary to achieve both gate current gate voltage limitations.
Currently, gate voltage limiting and transient voltage suppression (TVS) can be achieved with silicon Zener diodes. For group III-nitride based transistors, however, Zener diodes must be connected off-chip, which requires space for large wire-bond pads. Off-chip connection with wire-bonds limits the switching speed of the power devices. Zener diodes cannot be fabricated on the group III-nitride hetero-structure because the wide-bandgap group III-nitride materials are difficult to be doped heavily, which is needed to accommodate Zener breakdown voltage down to the ON-state critical Schottky gate voltage of group III-nitride power transistors (e.g., a typical value of about 2.5V).
The above-described background is merely intended to provide an overview of contextual information regarding group-III nitride heterojunction devices, and is not intended to be exhaustive. Additional context may become apparent upon review of one or more of the various non-limiting embodiments of the following detailed description.